This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The immunological response to vaccination against influenza after allogeneic hematopoietic stem cell transplantation (HSCT) or autologous HSCT is not well understood. The optimal time for seasonal vaccination post transplant has not been defined. Further, very little is understood about the memory response during immune reconstitution. Defining both the humoral and cellular immune response during hematopoietic reconstitution would allow better management of HSCT patients and protect these immuno-compromised patients against the morbidity of influenza infection. Studies in this patient population will yield a better understanding of the immune response to the influenza vaccine, giving insight into strategies to protect the overall population from a possible influenza pandemic.